The present invention relates to apparatus and methods for securing a motor vehicle and, in particular, to security systems that disable the car after unauthorized use.
Car thieves will sometimes directly confront or assault an owner and forcibly take the car. When confronted with such a threat the first concern of the owner should be escape. Safety considerations may require the owner to abandon the vehicle to the thief. Nevertheless, there is a need for vehicle security systems that will frustrate the car thief.
A conventional car security system may either sound an alarm or disable the automobile immediately at the time of theft. Such a system may be ineffective since an experienced car thief will recognize the existence of the automobile security system. The thief may take the time to circumvent the security system, since often the vehicle is parked at a location favorable to the thief. In the case of a forcible robbery in the presence of an owner, disabling the automobile immediately can be dangerous, since contact between the owner and thief is prolonged.
Known automotive security systems have proposed disabling an automobile after the elapse of a time interval measured by a timer. In a simple system such as U.S. Pat. No. 4,222,033 a delayed circuit breaker placed in series with the ignition coil will disable the coil in 10 to 30 seconds after the vehicle is started. This known system also will sound the car horn after the car is disabled. A disadvantage with this type of system is the dependence on elapsed time. The owner cannot be certain that the thief will immediately move the car and successfully avoid traffic so that the car will stall at a safe distance from the owner. If the disabled car remains near the owner the thief will still present a threat. See also U.S. Pat. Nos. 3,614,485; 4,485,887; and 4,866,296.
In U.S. Pat. No. 4,302,747 an electronic timer can disable a car after an unspecified amount of time. This known system is designed to be armed at all times unless manually disabled by the operator in advance. This system still has the disadvantage of responding only to elapsed time and not to actual motion of the motor vehicle.
In U.S. Pat. No. 3,907,060 a solenoid valve can stop the fuel flow and stall a stolen car. The system is designed to allow the vehicle to operate for awhile with the residual fuel left downstream of the closed solenoid valve. This system does not depend upon distance travelled and the stalling of the engine depends strictly on the residual capacity of the fuel system. See also U.S. Pat. Nos. 4,107,962; and 4,300,495.
In U.S. Pat. No. 4,162,716 the operating time of a vehicle having a closed solenoid valve is extended by employing a fuel reservoir downstream from the solenoid valve. Again this system is not distance responsive and requires a reservoir that can be a service problem.
Accordingly, there is a need for a security system for a motor vehicle that ensures that the motor vehicle will be moved a safe distance from the owner before stalling. To be practical, such a system must be reliable, fail safe and cost effective.